In the fabrication of microelectronic components, a number of the steps involved, for instance, in preparing integrated circuit chips and the packaging for the chips (articles to which the chips are attached and protected), are etching processes. Accordingly, over the years, a number of vastly different types of etching processes to remove material, sometimes in selective areas, have been developed and are utilized to varying degrees. Moreover, the steps of etching different layers which constitute, for instance, the finished integrated circuit chip are among the most critical and crucial steps.
One method widely employed for etching is to overlay the surface to be etched with a suitable mask and then immerse the surface and mask in a chemical solution which attacks the surface to be etched, while leaving the mask intact and while only etching other materials of the article to at most, a minimum extent.
In many structures, a silicon nitride layer exists on top or beneath a silicon dioxide layer and it becomes necessary to etch the silicon nitride without overetching the silicon dioxide. The ability to use a fluoride such as hydrogen fluoride in such situation presents a problem since hydrogen fluoride etches silicon dioxide at a much faster rate than it does silicon nitride. It would therefore be desirable to provide an etching procedure that achieves excellent removal of the silicon nitride and especially a procedure that exhibits an etching rate for silicon nitride that is at least as fast as the rate for silicon dioxide.